In an X-ray CT (Computed Tomography) device, which is one of medical image diagnosis devices, X rays generated from an X-ray tube passes through a test subject. An image is taken as a pair of X-ray detectors, which is so disposed as to face the X-ray tube, rotates around the test subject. As a result, a tomographic image of the test subject can be obtained. A portion that rotates the X-ray tube and a pair of X-ray detectors is referred to as a rotation unit. A portion that supports the rotation unit is referred to as a fixed unit. Conventionally, an exterior cover of the fixed unit mainly includes a front dome cover and a rear dome cover. An opening (gantry dome) is formed at a portion that a bed between the facing X-ray tube and the X-ray detectors enters. The above is formed by combining integral-molding parts or a plurality of parts.
Moreover, on an internal wall surface of the gantry dome, in order to prevent a test subject from putting a hand or the like into the high-speed rotation unit by accident, a dome cover sheet is provided as an X-ray irradiation window in terms of safety. Before being attached, the dome cover sheet is usually in the form of a sheet. The dome cover sheet is attached to the internal wall surface of the gantry dome, which is made up of the front dome cover and the rear dome cover, so as to be in the form of a cylinder. Depending on the product, the dome cover sheet may be in the form of a cylinder from the beginning. Accordingly, the dome diameter of the gantry dome, which is made by assembling the exterior covers, is fixed, and the configuration does not allow the dome diameter to vary.
If the distance between the X-ray tube and the X-ray detectors is reduced, magnification radiography becomes mechanistically available. The only way to carry out magnification radiography with the current dome-cover structure is to ensure a space inside the rotation unit by designing a small dome diameter from the beginning and shorten the distance (SID: Source Image Distance) between the X-ray tube and the X-ray detectors. However, when the dome diameter is simply made smaller as described above, for example, in the case where a test subject has a large physique or any other case, the problem is that it is not possible to meet the demand of increasing the dome diameter even at the time of normal radiography.
One embodiment of the present invention is to provide an X-ray CT device whose dome diameter is variable.